Is it climate change? Reaching its likely minimum extent for 2015, Arctic sea's minimum ice extent was the fourth lowest in the satellite record since observations from space began.

Is it climate change? Reaching its likely minimum extent for 2015, Arctic sea’s minimum ice extent was the fourth lowest in the satellite record since observations from space began.

The analysis by NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado at Boulder showed the annual minimum extent was 1.70 million square miles (4.41 million square kilometers) on Sept. 11. This year’s minimum is 699,000 square miles (1.81 million square kilometers) lower than the 1981-2010 average.

Arctic sea ice cover, made of frozen seawater that floats on top of the ocean, helps regulate the planet’s temperature by reflecting solar energy back to space. The sea ice cap grows and shrinks cyclically with the seasons.

Its minimum summertime extent, which occurs at the end of the melt season, has been decreasing since the late 1970s in response to warming temperatures.

In some recent years, low sea-ice minimum extent has been at least in part exacerbated by meteorological factors, but that was not the case this year.

This year is the fourth lowest, and yet people haven’t seen any major weather event or persistent weather pattern in the Arctic this summer that helped push the extent lower as often happens, said sea ice scientist Walt Meier, adding that it was a bit warmer in some areas than last year, but it was cooler in other places, too.

In contrast, the lowest year on record, 2012, saw a powerful August cyclone that fractured the ice cover, accelerating its decline.